SCI-FACTS ---> Your brain makes imaginary monsters when you stare in a mirror
Your brain only has the power to focus on so many things at once. All the senses are affected by this but sight especially. The mind tunes out everything that it isn't directly focusing on. In fact, the Troxler Effect is when you stare at one thing for a long enough time that other things in your vision fade out.
In an experiment with people staring into a mirror, they saw deformations of their own face, their parent's face with features changed, an animal face or a monstrous being.